• 지구물리와물리탐사
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• 제19권4호
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• pp.220-227
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• 2016

해양 탄성파 탐사를 통해 취득한 자료에는 지하 매질에서 반사되어 오는 신호뿐만 아니라 해수면에서 되반사되어 발생하는 고스트가 존재한다. 고스트는 특정 주파수 성분을 약화시켜 탄성파 자료의 시간 해상도를 저하시킨다. 고스트를 효과적으로 제거하기 위해서는 정확한 고스트의 지연시간과 해수면의 반사계수가 요구된다. 고스트 지연시간은 해수면의 상하 움직임, 에어건과 스트리머의 움직임 및 벌림(offset) 거리 등에 의해 변하며, 해수면의 반사계수도 주파수, 평면파의 입사각 그리고 해상 상태에 따라 변한다. 이러한 영향을 고려한 고스트 지연시간을 추정하기 위하여 이 연구에서는 고스트 제거 트레이스 및 이의 자기상관 자료의 L-1 norm, L-2 norm 그리고 첨도(kurtosis)를 비교하였다. 자기상관자료의 L-1 norm을 계산하여 고스트 지연시간을 추정하는 것이 오차가 가장 적게 발생하였다. 현장자료의 파고를 고려하고 키르히호프 근사식을 이용하여 해수면의 반사계수를 계산하여 음원 및 수신기 고스트 제거에 적용하였다. 고스트를 제거함으로써 약화된 주파수 성분을 복원하였으며 시간 해상도가 향상된 구조보정 단면을 얻었다.

• Steel and Composite Structures
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• 제43권2호
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• pp.139-152
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• 2022

Steel-reinforced concrete (SRC) L-shaped column is the vertical load-bearing member with high spatial adaptability. The seismic behavior of SRC L-shaped column is complex because of their irregular cross sections. In this study, the hysteretic performance of six steel truss reinforced concrete L-shaped columns specimens under the combined loading of compression, bending, shear, and torsion was tested. There were two parameters, i.e., the moment ratio of torsion to bending (γ) and the aspect ratio (column length-to-depth ratio (φ)). The failure process, torsion-displacement hysteresis curves, and bending-displacement hysteresis curves of specimens were obtained, and the failure patterns, hysteresis curves, rigidity degradation, ductility, and energy dissipation were analyzed. The experimental research indicates that the failure mode of the specimen changes from bending failure to bending-shear failure and finally bending-torsion failure with the increase of γ. The torsion-displacement hysteresis curves were pinched in the middle, formed a slip platform, and the phenomenon of "load drop" occurred after the peak load. The bending-displacement hysteresis curves were plump, which shows that the bending capacity of the specimen is better than torsion capacity. The results show that the steel truss reinforced concrete L-shaped columns have good collapse resistance, and the ultimate interstory drift ratio more than that of the Chinese Code of Seismic Design of Building (GB50011-2014), which is sufficient. The average value of displacement ductility coefficient is larger than rotation angle ductility coefficient, indicating that the specimen has a better bending deformation resistance. The specimen that has a more regular section with a small φ has better potential to bear bending moment and torsion evenly and consume more energy under a combined action.

• 지구물리와물리탐사
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• 제9권2호
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• pp.139-147
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• 2006

본 연구에서는 가스 하이드레이트 부존 예상지역인 한반도 동해 지역의 탄성파 탐사자료 처리 및 해석결과를 근거로 하여 가스 하이드레이트의 탄성파 탐사자료의 특성, 지층 정보 및 속도를 규명하기 위해서 탄성파 수치모형 실험을 실시하였다. Staggered grid를 이용한 유한차분법 탄성파 모델링 기법으로 통상적인 다중채널 탄성파 탐사, OBC 탐사 그리고 VCS 탐사에 대해여 적용하였다. 본 연구 결과 staggered grid를 이용한 유한차분법은 P파와 S파 그리고 밀도에 대한 변수를 자유롭게 적용할 수 있어서 심해저 가스 하이드레이트의 부존상황에 대한 탄성파 모델링 적용이 용이하였으며, 가스 하이드레이트의 부존 증거인 BSR (Bottom Simulating Reflector)과 같이 가스 하이드레이트층과 자유 가스(Free Gas)층 사이의 경계면에서 높은 임피던스 차이로 인한 큰 진폭의 반사파와 위상역전 현상을 관찰할 수 있었다. 그리고 수치모형 실험을 이용하여 획득한 자료에 대하여 수진기와 음원의 거리에 따른 반사계수를 계산하였으며 수치 모델링으로 획득한 인공합성 탄성파기록의 반사계수와 Shuey (1985)의 근사식에 의해 구해진 반사계수의 값이 거의 일치하였다.

• Earthquakes and Structures
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• 제26권5호
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• pp.349-361
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• 2024

Excessive torsional behaviour is one of the major reasons for failure of buildings, as inferred from past earthquakes. Numerous seismic codes across the world specify a displacement-based or drift-based criterion for classifying buildings as torsionally irregular. In recent years, quite a few researchers have pointed out some of the inherent deficiencies associated with the current codal guidelines on torsional irregularity. This short communication paper aims to envisage the need for a revision of the displacement-based guidelines on torsional irregularity, and further highlight the appropriateness of a rotation-based criterion. A set of 6 reinforced concrete building models with asymmetric shear walls are analysed using ETABS v18.0.2, by varying the number of stories from 1 to 9, and the torsional irregularity coefficient of various stories is calculated using the displacement-based formula. Since rotation about the vertical axis is a direct indication of the twist experienced by a building, the calculated torsional irregularity coefficients of all stories are compared with the corresponding floor rotations. The conflicting results obtained for the torsional irregularity coefficients are projected through five categories, namely mismatch with floor rotations, inconsistency in trend, lack of clarity in incorporation of negative values, sensitivity to low values of displacement and error conceived in the mathematical formulation. The findings indicate that the irregularity coefficient does not accurately represent the torsional behaviour of buildings in a realistic sense. The Indian seismic code-based values of 1.2 and 1.4, which are used to characterize buildings as torsionally irregular are observed to be highly sensitive to the numerical values of displacements, rather than the actual degree of rotation. The study thus emphasizes the revision of current guidelines based on a more relevant rotation-based or eccentricity-based approach.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.407-414
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• 2000

The friction pendulum type seismic isolation system (FPS) has been developed to provide a simple and effective way to achieve earthquake resistance for buildings . The major advantages are: the isolation frequency can be easily achieved by designing a curvature of the surface and does not depend on the supported weight of a structure. The function of carrying vertical load is separated to the function of providing horizontal stiffness. Next the friction provides sufficient energy dissipation to protect the structure from earthquake response and resistance to the weak external disturbances such as wind load and ground vibrations due to traffic. In this paper, the friction coefficients are evaluated from number of experiments on the FPS test specimens. The relations between friction coefficient and the test waveform, velocity, and pressure are reviewed and further works are discussed.

• Smart Structures and Systems
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• 제4권2호
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• pp.221-232
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• 2008

This paper represents the final results of a research program sponsored by the European Commission through project WIND-CHIME ($\underline{W}$ide Range Non-$\underline{IN}$trusive $\underline{D}$evices toward $\underline{C}$onservation of $\underline{HI}$storical Monuments in the $\underline{ME}$diterranean Area), in which the possibility of using advanced seismic protection technologies to preserve historical monuments in the Mediterranean area is investigated. In the current research, the dynamic characteristics of two outstanding Mamluk-Style minarets, which similar minarets were reported to experience extensive damage during Dahshur 1992 earthquake, are investigated. The first minaret is the Qusun minaret (1337 A.D, 736 Hijri Date (H.D)) located in El-Suyuti cemetery on the southern side of the Salah El-Din citadel. The minaret is currently separated from the surrounding building and is directly resting on the ground (no vaults underneath). The total height of the minaret is 40.28 meters with a base rectangular shaft of about 5.42 ${\times}$ 5.20 m. The second minaret is the southern minaret of Al-Sultaniya (1340 A.D, 739 H.D). It is located about 30.0 meters from Qusun minaret, and it is now standing alone but it seems that it used to be attached to a huge unidentified structure. The style of the minaret and its size attribute it to the first half of the fourteenth century. The minaret total height is 36.69 meters and has a 4.48 ${\times}$ 4.48 m rectangular base. Field investigations were conducted to obtain: (a) geometrical description of the minarets, (b) material properties of the minarets' stones, and (c) soil conditions at the minarets' location. Ambient vibration tests were performed to determine the modal parameters of the minarets such as natural frequencies and mode shapes. A $1/16^{th}$ scale model of Qusun minaret was constructed at Cairo University Concrete Research Laboratory and tested under free vibration with and without SMA wire dampers. The contribution of SMA wire dampers to the structural damping coefficient was evaluated under different vertical loads and vibration amplitudes. Experimental results were used along with the field investigation data to develop a realistic 3-D finite element model that can be used for seismic risk evaluation of the minarets. Examining the updated finite element models under different seismic excitations indicated the vulnerability of such structures to earthquakes with medium to high a/v ratio. The use of SMA wire dampers was found feasible for reducing the seismic risk for this type of structures.

• 한국지반환경공학회 논문집
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• 제10권1호
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• pp.49-54
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• 2009

지진동에 대한 사면의 안정성은 일반적으로 지진계수를 이용하여 지진하중을 유사정적 하중으로 단순화하여 한계평형법으로 평가된다. Transient 지진동은 지진계수를 이용하여 정적하중으로 대체된다. 하지만, 유사정적 해석결과에 절대적인 영향을 미치는 지진계수는 합리적인 물리적 근거 없이 산정된다. 또한 내진설계기준에 의거하여 산정되는 최대가속도는 사면의 진동특성을 반영한다고 볼 수 없으며, 이를 정확하게 예측하기 위해서는 2차원 동적해석을 수행해야 한다. 본 연구에서는 수정된 1차원 동적해석과 유사정적해석을 연결한 Hybrid 유사정적 해석법을 제안하였다. 기존의 해석기법은 깊이에 따라서 변이하는 가속도를 고려할 수 없기에 신뢰성 있는 사면의 안정성 예측이 어려운 실정이다. 수정된 1차원 지반응답해석은 깊이에 따른 사면 무게변화를 모델링하기 위하여 층의 밀도를 조정하였으며 위치별 진동가속도를 예측하기 위해서 다수의 해석을 수행하였다. 2차원 유한요소해석과 비교한 결과, 수정된 1차원 해석은 2차원 해석과 일치성이 우수한 것을 확인할 수 있었다. 해석결과를 유사정적해석에 입력하여 깊이에 따라서 변이하는 가속도 주상도를 적용하였으며 기존의 해석방법으로 계산된 안전율과 비교하였다. 비교 결과, 계산된 안전율에는 큰 차이가 발생하는 것으로 나타났으며, 기존의 해석기법으로 안전율을 예측할 경우, 매우 비현실적인 값을 계산할 수 있다. 본 연구에서 개발된 기법은 해석의 신뢰성을 현격하게 향상시키는 것으로 나타났다.

• Earthquakes and Structures
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• 제12권1호
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• pp.135-144
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• 2017

Near-fault ground motions are characterized by high values of the ratio between the peak of vertical and horizontal ground accelerations, which can significantly affect the nonlinear response of a base-isolated structure. To check the effectiveness of different base-isolation systems for retrofitting a r.c. framed structure located in a near-fault area, a numerical investigation is carried out analyzing the nonlinear dynamic response of the fixed-base and isolated structures. For this purpose, a six-storey r.c. framed building is supposed to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by current Italian code in a high-risk seismic zone. In particular, elastomeric (e.g., high-damping-laminated-rubber bearings, HDLRBs) and friction (e.g., steel-PTFE sliding bearings, SBs, or friction pendulum bearings, FPBs) isolators are considered, with reference to three cases of base isolation: HDLRBs acting alone (i.e., EBI structures); in-parallel combination of HDLRBs and SBs (i.e., EFBI structures); FPBs acting alone (i.e., FPBI structures). Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffnesses of the HDLRBs, sliding ratio, defined as the global sliding force divided by the maximum sliding force of the SBs, and in-plan distribution of friction coefficient for the FPs are investigated. The EBI, EFBI and FPBI base-isolation systems are designed assuming the same values of the fundamental vibration period and equivalent viscous damping ratio. The nonlinear dynamic analysis is carried out with reference to near-fault earthquakes, selected and scaled on the design hypotheses adopted for the test structures.

• Earthquakes and Structures
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• 제17권3호
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• pp.245-256
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• 2019

An experimental study was conducted to evaluate the dynamic behavior of a free-standing frame equipped with a movable base system using cast iron and mortar as the bearing materials. The preliminary friction test indicated that a graphite layer developed on the interface and exhibited stable friction behavior. The friction coefficient ranged from 0.33 to 0.36 when the applied normal compression stress ranged from 2.6 to 5.2 MPa. The effect of the variation of normal compression stress would be small. Shaking table tests on the free-standing frame showed that rock, slide, and rock-slide responses occurred. The cumulative slide distance reached 381 mm under JMA Kobe wave excitation; however, only a few cyclic slides occurred at the same locations along the moving track. Most surfaces sustained single slides. Similar results can be observed in other shaking conditions. The insufficient cyclic sliding and significant rocking resulted in a few graphite layers on the mortar surfaces. Friction coefficients were generally similar to those obtained in the preliminary friction tests; however, the values fluctuated when the rocking became significant. The collisions due to rocking caused strong horizontal acceleration responses and resulted in high friction coefficient. In addition, the strong horizontal acceleration responses caused by the collisions made the freestanding specimen unable to reduce the input horizontal acceleration notably, even when slippage occurred. Compared with the counterpart fixed-base specimen, the specimen equipped with the iron-mortar base could reduce the horizontal acceleration amplification response and the structural deformation, whereas the vertical acceleration response was doubled due to collisions from rocking.

• 한국공간구조학회논문집
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• 제8권1호
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• pp.57-67
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• 2008

건축구조물의 응답스펙트럼 해석법은 주로 내진설계를 위하여 많이 사용되고 있고 시간이력 해석법은 기계, 설비, 사람에 의한 하중 등이 건축물에 가해지는 경우에 많이 사용되고 있다. 응답스펙트럼 해석법과 시간이력해석법을 비교해 보면 시간이력 해석법은 복잡하고 분석이 어려우며 해석에 시간을 많이 필요로 하고 구조물이 복잡해질 경우에는 해석이 어려운 경우도 있다. 본 연구에서는 응답스펙트럼해석법을 이용하여 기계나 사람에 의한 하중을 받는 건축물 바닥판의 연직응답을 구하고자 한다. 이를 위하여 모드조합에서는 CQC기법을 적용하였으며, 사람의 활동을 중심으로 하중간의 상관관계를 분석하여 해석에 적용하였다. 제안방법은 시간이력해석결과와도 비교하였으며 하중간의 상관계수는 복수의 하중을 받는 바닥판구조물의 응답스펙트럼 해석에 반드시 고려해야 하는 결과를 얻었다.